Interpretive Summary: Glucagon-like peptide-2 (GLP-2) is a gut hormone secreted from endocrine cells in the gut and neurons in the brain. GLP-2 stimulates intestinal crypt cell proliferation and mucosal blood flow while decreasing stomach emptying and intestine motility. However, molecular mechanisms for GLP-2-mediated actions have not been established. We defined that GLP-2 enhances electric activities of Ca2+ channels through activating protein kinase A signaling, partially stimulating glucose uptake by brain neurons. This finding is important because that GLP-2-induced increase in intracellular Ca2+ flux may be physiologically relevant to neurotransmitter release and hormone secretion.

Technical Abstract:
Glucagon-like peptide-2 (GLP-2) is a neuropeptide secreted from endocrine cells in the gut and neurons in the brain. GLP-2 stimulates intestinal crypt cell proliferation and mucosal blood flow while decreasing gastric emptying and gut motility. However, a GLP-2-mediated signaling network has not been fully established in primary cells. Since the GLP-2 receptor mRNA and protein were highly expressed in the mouse hippocampus, we further characterized that human 125I-labeled GLP-21–33 specifically bound to cultured hippocampal neurons with Kd = 0.48 nM, and GLP-2 acutely induced subcellular translocalization of the early gene c-Fos. Using the whole cell patch clamp, we recorded barium currents (IBa) flowing through voltage-gated Ca2+ channels (VGCC) in those neurons in the presence of GLP-2 with and without inhibitors. We showed that GLP-2 (20 nM) enhanced the whole cell IBa mediated by L-type VGCC that was defined using an L-type Ca2+ channel blocker (nifedipine, 10 µM). Moreover, GLP-2-potentiation of L-type VGCC was abolished in neurons pretreated with a PKA inhibitor (PKI14–22, 1 µM). Finally, using a fluorescent nonmetabolized glucose analog (6-NBDG) tracing imaging, we showed that glucose was taken up directly by cultured neurons. GLP-2 increased 2-deoxy-D-[3H]glucose uptake that was dependent upon dosage, activation of PKA, and potentiation of L-type VGCC. We conclude that GLP-2 potentiates L-type VGCC activity through activating PKA signaling, partially stimulating glucose uptake by primary cultured hippocampal neurons. The potentiation of L-type VGCC may be physiologically relevant to GLP-2-induced neuroendocrine modulation of neurotransmitter release and hormone secretion.